<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			body {
				margin: 0;
			}

			.c1 {
				/* border: 10px solid red; */
				width: 20px;
				height: 0px;
				/* margin: 10px; */
				padding: 10px;

				border-top: 5px solid blue;
				border-bottom: 5px solid green;
				border-left: 5px solid yellow;
				border-right: 5px solid aqua;
			}

			.c2 {
				border: 1px solid blue;
				/* margin: 15px; */
				padding: 15px;
			}
		</style>
	</head>
	<body>
		<!--
		    1. div盒子独占一行 ,默认没高度，会被撑开
		    2. 宽度是浏览器宽
			3.
		-->
		<div class="c1">123</div>
		<div class="c2">ABC</div>
	</body>
</html>
